Delete old bootmgr file

I'm trying to remove a directory containing Windows 10 installation files as taken from the ISO image.

BOOTMGR refuses to be removed, claiming I need administrator privileges, yet I am logged in as an administrator at the time.

I have tried in safe mode (which allowed me to remove all other files in the directory), using both the command prompt and windows UI, to no avail.

I caot change the permissions on the file, even though I am the owner.

Short of using a live linux system with RW on NTFS drives, I'm lost as to how to go about this.

Any suggestions on how to remove the old BOOTMGR file would be appreciated.